U.S. Pat. No. 2,899,191 discloses a weighing scale in which a weighing platform is supported on a pair of beams. The beams are supported adjacent their outer ends on knife edges, and the platform is supported on the beams by journals comprising pins mounted in lugs, the pins being spaced inwardly equal distances from the knife edges. A strain gauge is mounted at the centre of each beam.
Such an arrangement has the advantage that, in principle, the bending moment at the centre of the beam will be proportional to the sum of the forces applied to the journal pins, so that measuring the strain at the centre of each beam will provide a measure of the total load on the platform.
An arrangement such as that described in the Hunt U.S. patent, is found to suffer from serious disadvantages as a result of the manner of support and of application of load to the beams on which the strain gauges are mounted. Thus, for example, any misalignments, and slope or uneveness in the supporting surface will be transmitted as twisting or bending forces to the beam, and significant inaccuracy may result.
In U.S. patent specification No. 4,287,958 another approach to load summation using a similar configuration of forces and strain gauge is disclosed, in this case in the form of a load measuring vehicle suspension. In this specification the load receiving journals are located so that their axes intersect the beam axis, and are provided by elastomeric bushings on stub shafts which extend on either side of the beam at each of the load application points. As the journals are located outwardly of the beam, however, the arrangement is prone to the production of twisting forces which will interfere with accurate measurement. Furthermore, the manner in which the ends of the beam in this disclosure are mounted, encourages the transmission to the beam of torsional forces, as well as spurious bending moments, from these mountings wherever misalignment occurs.